1. Field of the Invention
The present invention relates to an organic domain/inorganic domain hybrid material and use thereof. More particularly, the present invention is concerned with an organic domain/inorganic domain hybrid material comprising: an organic domain comprising at least one water-soluble organic polymer having a plurality of functional groups, wherein each functional group is independently selected from the group consisting of an anionic functional group and a cationic functional group, and an inorganic domain. The organic domain and the inorganic domain are chemically bonded to each other through the functional groups of the organic polymer. The inorganic domain comprises a plurality of inorganic bridges having both ends thereof which are, respectively, chemically bonded to the functional groups of the organic polymer, wherein each inorganic bridge independently comprises at least one silicon atom, at least two oxygen atoms and at least one divalent metal atom, wherein the silicon atom(s) and the oxygen atoms together form at least one siloxane linkage which is arranged longitudinally of the inorganic bridge, wherein each divalent metal atom is ionically bonded to the oxygen atoms of the siloxane linkages positioned adjacent to the divalent metal atoms, wherein, when at least a part of the organic domain is comprised of at least one organic polymer having an anionic functional group and optionally a cationic functional group, the weight ratio of the organic domain to the inorganic domain is less than 1.0. The present invention is also concerned with a hydrophilicity reagent comprising the above-mentioned hybrid material; an antibacterial/antifungal reagent comprising the above-mentioned hybrid material; a hydrophilic coating composition comprising an aqueous dispersion (or emulsion) of an organic polymer and, dispersed therein, the above-mentioned hydrophilicity reagent; and a hydrophilic coating formed from the hydrophilic coating composition. The hybrid material of the present invention not only has many excellent functional properties (such as hydrophilicity and antibacterial property), which are ascribed to the component elements, component molecules, structure and the like of the hybrid material, but also can be easily produced. The hybrid material of the present invention is advantageous not only in that the hybrid material per se can be used as a functional material, but also in that the hybrid material can be used as a functional additive which is added to another organic or inorganic material so as to impart that material with hydrophilicity and/or antibacterial activity. Thus, the hybrid material is a commercially very valuable material.
2. Prior Art
Recently, vigorous studies have been made on hybrid materials each comprising a combination of at least two materials which are different in properties, because such hybrid materials exhibit excellent properties which cannot be obtained by a non-hybrid, single material. Among such hybrid materials, those comprising a combination of an organic polymeric material and an inorganic material have been attracting attention. Especially, with respect to the so-called “nano-composite material” (comprising a hybrid of an organic polymeric material and an inorganic material, in which the organic polymeric material or the inorganic material is present in the form of nanometer-size domains), such nano-composite material exhibits unique properties ascribed to its unique structure, and hence, the development of applications of the nano-composite material is expected.
As examples of widely known nano-composite materials, there can be mentioned a hybrid material obtained by uniformly dispersing a lamellar silicate (e.g., clay) as an inorganic material in a polyamide resin as an organic polymeric material (see A. Usuki et al., J. Mater. Res., 8, [5], 1179 (1993)), and a material composed of silica and an organic molecule (either of which is the main component), in which respective nano-size particles of silica and an organic molecule are mutually, finely dispersed, and which is produced by subjecting a silicon alkoxide as a raw material to sol-gel process in the presence of an organic molecule (oligomer or polymer) to form a silica (see Novak, M., Adv. Mater. 5,422 (1993) and Chujo, Y., and Encyclp. Poly. Sci. Tech., CRC Press, Boca Raton, 6, 4793 (1996)). These documents describe how to improve the mechanical properties of nano-composite materials or how to produce an intermediate of a porous silica. These documents do not however disclose a technique to produce a hybrid material exhibiting high hydrophilicity.
Therefore, studies have been made to produce a hybrid material having high hydrophilicity. For example, a hybrid material composed mainly of an inorganic material, in which a water-soluble polymer (such as polyacrylic acid or polymethacrylic acid) is intercalated between the layers of calcium silicate hydrate, has been developed (see H. Matsuyama et al., Chemistry of Materials, 11, 16–19 (1999)). With respect to this hybrid material, the use of calcium silicate hydrate which is a cement hydrate is an essential feature, and it has not been attempted to impart the hybrid material with various functions by using an inorganic material composed of essential elements other than those of a cement hydrate or by using a copolymer as an organic material. Further, there has been no document disclosing a technique to use the hybrid material as an additive to impart hydrophilicity to other materials.
On the other hand, a hydrophilized coating composition has been attracting attention as a coating composition having stain resistance wherein dirt on a coating formed from the coating composition can be easily washed away with water, such as rainwater, to prevent the dirt from adhering to the coating, and wherein occurrence of the so-called “raindrop dirt” (i.e., oily dirt adhering to the coating, which is formed along the path of flow of a raindrop) can be suppressed. Especially, in the field of aqueous coatings which have a low odor emission and are suitable for use at a construction site, it has been expected to develop a coating composition capable of forming a stain resistant coating, which can be used without cumbersome operations, such as a multiple coating operation and a mixing of liquid components of the coating composition at the construction site.
Recently, a number of coatings using a photocatalyst, such as titanium oxide, have been developed. However, when a photocatalyst is mixed with an organic substance, the organic substance is decomposed due to the oxidative activity of the photocatalyst. Therefore, when a photocatalyst is used in a coating composition, the photocatalyst needs to be used in combination with an inorganic material as a binder. Therefore, such a photocatalyst-containing coating composition is disadvantageous in that a coating formed from the composition is likely to suffer cracking, and that it becomes necessary to form a layer of an inorganic material on an undercoating for the photocatalyst-containing coating composition. Thus, the use of the photocatalyst-containing coating composition for coating an outer wall has serious problems from the viewpoint of workability and cost.
With respect to a technique to hydrophilize a coating composition by using a hybrid material, Unexamined Japanese Patent Application Laid-Open Specification No. 2000-264971 discloses a technique to modify the surface of a polymer in a polymer emulsion with an organosilicon compound; however, this technique has a problem that the production of the coating composition becomes complicated. Further, WO99/05228 discloses a technique in which a silicon alkoxide is mixed as a hydrophilicity reagent with a polymer emulsion to obtain a hydrophilic coating composition which can be used for forming a stain resistant coating. However, alkoxides undego hydrolysis when contacted with water, so that the hydrophilic coating composition has a disadvantageously short pot life (less than one day). Therefore, the use of such a hydrophilic coating is difficult from a practical point of view.
Further, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 9-227118 (corresponding to U.S. Pat. No. 5,786,417) discloses a method using a method in which an organic clay composite (comprising clay layers and polyalkylene oxide position between and bonded to the clay layers) is used as a thickner for an aqueous coating composition. However, a coating obtained by this technique is not hydrophilized and does not have stain resistance.
As a material having an antibacterial property, there is known an inorganic material-containing antibacterial reagent using a metal (e.g., silver or copper) having an antibacterial property or a sterilizing organic compound having a specific chemical structure.
For example, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 9-30915 discloses a sintered material obtained by calcining a material comprising a silica gel (as a substrate) having carried thereon an antibacterial metal, such as silver or copper. However, this method involves a complicated operation for calcination, and hence, the productivity of the desired material is not satisfactorily high. In addition, the amount of the antibacterial metal which can be contained in the material is only several % by weight.
Further, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 10-130105 (corresponding to U.S. Pat. No. 5,876,738) discloses a method for obtaining a lamellar silicate (carrier) having an organic antifungal material supported between the layers of the lamellar silicate. However, the resultant product in which the organic substance is simply supported between the layers of the lamellar silicate cannot maintain the desired effect for a satisfactorily long period of time.
Further, recently, materials using a photocatalyst have been widely studied. For example, Unexamined Japanese Patent Application Laid-Open Specification No. 2000-17356 (corresponding to U.S. Pat. No. 6,313,064) discloses a photocatalyst alloy comprising copper and titanium. However, a photocatalyst is effective only at a location (such as near a bright window) exposed to direct sunlight, and cannot exhibit a satisfactory effect in so-called wet areas (such as a bath room and a kitchen) due to lack of light.
Thus, there has not been proposed an excellent organic/inorganic hybrid material which has various functional properties, such as hydrophilicity and antibacterial property, which can be easily produced and used.